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# There are trains travelling on 4 parallel tracks. The frequencies of

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Senior Manager
Joined: 10 Apr 2012
Posts: 269
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There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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24 Jun 2013, 12:41
2
2
00:00

Difficulty:

95% (hard)

Question Stats:

42% (02:05) correct 58% (01:39) wrong based on 155 sessions

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There are trains travelling on 4 parallel tracks. The frequencies of trains traveling on these tracks at equal interval of time are 4, 6, 8, 12 per hour respectively. If all trains start at 7 AM, after how much time will all the trains start together from the same place?

A. 1 Hour
B. 12 Hours
C. 24 Hours
D. 1/2 hours
E. 1/4 Hours
Director
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Location: India
Concentration: General Management, Operations
GMAT 1: 700 Q50 V34
GPA: 3.6
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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24 Jun 2013, 14:30
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2
guerrero25 wrote:
There are trains travelling on 4 parallel tracks. The frequencies of trains traveling on these tracks at equal interval of time are 4, 6, 8, 12 per hour respectively. If all trains start at 7 AM, after how much time will all the trains start together from the same place?

A. 1 Hour
B. 12 Hours
C. 24 Hours
D. 1/2 hours
E. 1/4 Hours

hi
1st track frequency is 4 trains/hr= every 15 min 1 train will leave
2nd track frequency is 6 trains/ hr = every 10 min 1 train will leave
3rd track frequency is 8 trains/hr= every 7.5 min 1 train will leave
4th track frequency is 12 trains /hr= every 5 min 1 train will leave

the time when each track train will leave at same time next time will be X mins (after 7 am)= =>where X=LCM of (15/10/7.5/5)=30 mins=1/2 hrs.
hence D.
KUDOS If it helped
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##### General Discussion
Senior Manager
Joined: 13 May 2013
Posts: 429
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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08 Aug 2013, 12:50
There are trains traveling on 4 parallel tracks. The frequencies of trains traveling on these tracks at equal interval of time are 4, 6, 8, 12 per hour respectively. If all trains start at 7 AM, after how much time will all the trains start together from the same place?

This is, more or less, a question regarding lowest common multiples. The LCM of 15, 10, 7.5 and 5 is 30.

4 train every 15 minutes
6 train every 10 minutes
8 train every 7.5 minutes
12 train every 5 minutes

ANSWER: D. 1/2 hours
Senior Manager
Joined: 10 Jul 2013
Posts: 315
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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08 Aug 2013, 13:07
guerrero25 wrote:
There are trains travelling on 4 parallel tracks. The frequencies of trains traveling on these tracks at equal interval of time are 4, 6, 8, 12 per hour respectively. If all trains start at 7 AM, after how much time will all the trains start together from the same place?

A. 1 Hour
B. 12 Hours
C. 24 Hours
D. 1/2 hours
E. 1/4 Hours

..................
after leaving,
the schedule(min) of 2nd train for 4lines= 15min 10min 7.5min 5min
LCM = 30 mins . so 1/2 hour(D) Answer
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Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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20 Nov 2013, 00:19
Quote:
15min 10min 7.5min 5min
LCM = 30 mins . so 1/2 hour(D) Answer

Can anyone please explain how to get the LCM. I am trying but i am getting 150.

15, 10, 75/10, 5
LCM of 15,10,75,5 and HCF of 1,1,10,1 = 150/1

Thanks & Regards
Vinni
Manager
Joined: 14 Dec 2011
Posts: 74
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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22 Nov 2013, 10:13
vinnik wrote:
Quote:
15min 10min 7.5min 5min
LCM = 30 mins . so 1/2 hour(D) Answer

Can anyone please explain how to get the LCM. I am trying but i am getting 150.

15, 10, 75/10, 5
LCM of 15,10,75,5 and HCF of 1,1,10,1 = 150/1

Thanks & Regards
Vinni

Please help on this one. I will really appreciate. How to get LCM as 30. I am getting 150.

Vinni
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Concentration: Finance, Marketing
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Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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13 Dec 2013, 07:16
vinnik wrote:
vinnik wrote:
Quote:
15min 10min 7.5min 5min
LCM = 30 mins . so 1/2 hour(D) Answer

Can anyone please explain how to get the LCM. I am trying but i am getting 150.

15, 10, 75/10, 5
LCM of 15,10,75,5 and HCF of 1,1,10,1 = 150/1

Thanks & Regards
Vinni

Please help on this one. I will really appreciate. How to get LCM as 30. I am getting 150.

Vinni

Hi,
You have to reduce the fraction 75/10 into its lowest term, i.e 15/2
LCM of 15,10,15,5 and HCF of 1,1,2,1 = 30/1
LCM = 30

Hope that helps..
Intern
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Joined: 11 Jul 2013
Posts: 27
Location: India
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GMAT 1: 660 Q49 V31
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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13 Dec 2013, 21:02
1
vinnik wrote:
vinnik wrote:
Quote:
15min 10min 7.5min 5min
LCM = 30 mins . so 1/2 hour(D) Answer

Can anyone please explain how to get the LCM. I am trying but i am getting 150.

15, 10, 75/10, 5
LCM of 15,10,75,5 and HCF of 1,1,10,1 = 150/1

Thanks & Regards
Vinni

Please help on this one. I will really appreciate. How to get LCM as 30. I am getting 150.

Vinni

I found following approach to be much simpler for calculating LCM which involves a decimal number :

LCM(15,10,7.5,5) - multiply the decimal number by 10 (it is done to take decimal out of the picture) and subsequently multiply other numbers as well with 10.

So, now what you are left with is to find LCM (150,100,75,50) , which comes to be 300.

Now divide 300 with the 10 you multiplied your original number set with and that will give you your original LCM, which is 30.

Hope you find it useful.
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Manager
Joined: 14 May 2015
Posts: 52
Re: There are trains travelling on 4 parallel tracks. The frequencies of  [#permalink]

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06 May 2017, 12:31
1/4, 1/6,1/8,1/12 hour per train
lcm of 1/4, 1/6,1/8,1/12=1/2
ans:D
Re: There are trains travelling on 4 parallel tracks. The frequencies of &nbs [#permalink] 06 May 2017, 12:31
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# There are trains travelling on 4 parallel tracks. The frequencies of

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